A P2X7R Single Nucleotide Mutation Promotes Chronic Allograft Vasculopathy

Heart transplantation is a lifesaving procedure however, more then 20% of patients do not survive beyond 3 years, being the cardiac allograft afflicted by cardiac allograft vasculopathy (CAV), which results in allograft loss. The purine adenosine 5'-triphosphate (ATP), released during cell damage/inflammation, is sensed by the ionotropic purinergic P2X7 receptor (P2X7R), which is expressed primarily, though not exclusively, on lymphocytes, thus regulating T cell activation. Loss-of-function single nucleotide mutations (SNPs) have been detected for P2X7R gene; particularly the Glu496 to Ala 1513A>C (rs3751143) P2X7R loss-of-function mutation is relatively common (1-3% of individuals are mutated omozygous and 25% are heterozygous). Our central hypothesis is that a loss-of-function P2X7R mutation identifies a group of cardiac transplanted patients at high risk for CAV and cardiac allograft loss because of a compensatory overexpression of P2X1R/P2X4R, which induces a disregulation of T-bet/ROR-g, ultimately leading to the abnormal generation of Th1/Th17 cells. Our primary goal is to define the effect of the P2X7R loss-of-function mutation on clinical end points in the CTOT-05 cohort of cardiac transplant recipients (200 patients) and to explore the effects of the mutation on the immune system. Our preliminary data demonstrated that P2X7R increases during cardiac transplant rejection in vivo in mice and in humans and it is activated by ATP released by cardiac cells, thus triggering activation of Th1/Th17 cells. However, while short-term disruption of the P2X7R pathway prolongs cardiac allograft survival, the genetic deletion of P2X7R accelerates CAV and shortens cardiac allograft survival. This was evident in P2X7R KO-B6 mice and in a group of cardiac transplant recipients bearing the P2X7R loss-of-function mutation. Based on our published results and our novel observations, we have developed the following working hypothesis: P2X7R loss-of-function mutation generates a compensatory overexpression of the other ionotropic purinergic receptors (P2X1/P2X4) with chronic delivery of ATP immunity, hyperactivation T-bet/ROR-g, abnormal generation of Th1/Th17 cells and ultimately leading to accelerated CAV and to cardiac allograft loss. To test this hypothesis, we will follow two main paths: i) we will evaluate in the CTOT-05 cohort of cardiac transplant recipients the effect of the Glu496 to Ala 1513A>C (rs3751143) P2X7R loss-of-function mutation on clinical end points (development of coronary artery vasculopathy, death, re-transplantation or re-listed for transplantation, any rejection) in the first year post transplant; ii) we will explore in vivo and ex vivo in the CTOT-05 cohort of cardiac transplant recipients the effects of P2X7R loss-of-function mutation on the immune system.